The broad, long term goals of the proposed research include an understanding of the way in which visual signal transduction occurs on a molecular level, particularly the functional role(s) of hydrophobic posttranslational modifications (via isoprenylation) of key proteins involved in visual signal transduction. Proteolytic processing of isoprenylated proteins represents a key step in the isoprenylation pathway. A novel endoprotease with specific activity toward isoprenylated proteins has been identified, but has yet to be isolated and characterized. The goals for the period of requested support are to purify this novel isoprenylated protein endoprotease in order to determine its mechanistic class, to determine the nature of active site residues through photoaffinity labeling studies, and to begin to clone and sequence the enzyme in an effort to determine the nature of possible isoforms of the enzyme. These experiments will allow for the further definition of the physiological role(s) of this enzyme and allow for the design of potent mechanism-based inhibitors,